implemented recurrence exception (EXDATE) support for custom events, refactored timetable break and holiday generation logic, and refined RRule editor UI/theming and tile layouts

lib/view/pages/timetable/details/custom_event_sheet.dart

@@ -7,6 +7,7 @@ import '../../../../widget/centered_leading.dart';
 import '../../../../widget/debug/debug_tile.dart';
 import '../../../../widget/details_bottom_sheet.dart';
 import '../custom_events/custom_event_edit_dialog.dart';
+import '../data/rrule_with_exceptions.dart';
 import 'delete_custom_event.dart';
 
 class CustomEventSheet {
@@ -78,7 +79,13 @@ class CustomEventSheet {
                 return const Text('Keine weiteren Vorkommnisse');
               }
               if (snapshot.data == null) return const Text('...');
-              final rrule = RecurrenceRule.fromString(event.rrule);
+              // Strip the rrule_generator-specific `;EXDATE=…` suffix
+              // first — `package:rrule` is strict and throws on it.
+              final parsed = parseRRuleWithExceptions(event.rrule);
+              if (parsed.rule.isEmpty) {
+                return const Text('Keine weiteren Vorkommnisse');
+              }
+              final rrule = RecurrenceRule.fromString(parsed.rule);
               if (!rrule.canFullyConvertToText) {
                 return const Text('Keine genauere Angabe möglich.');
               }